Croque Monsieur

Mornay sauce: In a medium pot over medium heat, add butter and cook until the butter is melted and starts to bubble. Add the all-purpose flour and whisk to combine the two. Allow the flour and butter to cook for 1 to 2 minutes, stirring often. 

Slowly add milk while continuing to whisk. Whisking frequently will help make sure that there are no lumps in your final sauce. Once all the milk has been added, cook the sauce for 4 to 5 minutes until it starts to thicken. 

Add the shredded cheese, salt, pepper, and nutmeg while continuing to whisk. Once the seasonings are fully incorporated and the sauce has thickened, you can remove the pot from the heat. If you are making your sandwich immediately you can add the lid to the pot to keep it warm while you prep everything else. 

Ham and cheese sandwich: Add mustard (if using) to one slice of the bread. Top the mustard with slices of ham and then top the ham with 2 to 4 tablespoons of shredded cheese. Close the sandwich with the second piece of bread.

Griddle sandwich: In a medium-sized pan over medium-low heat, add 1/2 tablespoon of butter. When the butter is fully melted add your ham and cheese sandwich. Cook this first side until it has browned and is toasty, somewhere between 3 and 6 minutes (check often). When the first side is browned remove the sandwich from the pan briefly, add the other half of the butter to the pan, and when it has melted add the sandwich back in on top of the melted butter untoasted side down. Toast this second side for 3 or 4 minutes until it is also fully toasted.

Remove the sandwich to a cooling rack while you prepare the next ingredients.

Turn on the broiler in your oven and allow it to preheat.  

Broiling: add mornay sauce to the top of the sandwich and then top the mornay with extra shredded cheese. Make sure you go all the way to the edges with the mornay sauce so that the bread does not burn in the broiler. 

Broil the sandwich in the oven for 3 to 5 minutes or until everything is melty and the cheese on top starts to turn brown and is very bubbly. Remove the sandwich to the cooling rack again to rest before serving.

Top the sandwich with finely chopped chives and serve.